This application relates to disease resistance in Vitis.
Grape (Vitis spp.) is a deciduous temperate fruit crop of ancient origin. Grape production (65 .times.10.sup.6 metic tons) exceeds that of any other temperate fruit crop and ranks after Citrus and banana among all fruit crops worldwide (FAO Production Yearbook, 1990). Grape surpasses all other fruit crops in value due to its multiple uses for fresh fruit, juice, jelly, raisins, and wine. For example, in the United States, seedless grapes represent about 80% and 98% of the total table and raisin grape production; respectively (In: 1994-95: The Distribution and Per Capita Consumption of California Table Grapes By Major Varieties in the United States and Canada, California Table Grape Commission, Fresno, Calif. 1995). Only a few seedless cultivars make up this production, of which `Thompson Seedless` is the most important. This cultivar accounts for the most production of any single grape variety in the United States. In 1992, `Thompson Seedless` was grown on 263,621 acres in California (In: California Grape Acreage, California Agricultural Statistics Service, Sacramento, Calif., 1993). Thirty-five percent of the table grape production in California in 1994 was `Thompson Seedless` (23,244,683 boxes, 10 kg/box). In 1993, 97% of the grapes grown for raisin production was `Thompson Seedless` (In: Raisin Committee Marketing Policy 1994-95, Raisin Administrative Committee, Fresno, Calif., 1994).
Although Vitis spp. is generally considered to have desirable fruit quality, it is susceptible to many pests and diseases, including anthracnose, black rot, botrytis bunch rot, crown gall, downy mildew, eutypa dieback, various nematodes, phomopsis cane and leaf spot, phylloxera, Pierce's disease, and powdery mildew. Hybridization with resistant species has been the only method available to produce resistant cultivars (Galet and Morton, In: Compendium of Grape Diseases, R. C. Pearson and A. C. Goheen, eds., APS Press, St. Paul, 1990, pp. 2-3). While improving grape is possible by conventional breeding, it is difficult and time consuming due to the two- to three-year generation cycle, the long period of time required for reliable progeny testing and selection, and inbreeding depression that prohibits selfing (Gray and Meredith, In: Biotechnology of Perennial Fruit Crops, F. A. Hammerschlag and R. E. Litz, eds., C.A.B. Intl., Wallingford, U.K. 1992). These characteristics make introgression of desirable traits into existing grape cultivars difficult if not impossible to achieve in an individual breeder's lifetime. Thus, the alternative, and potentially less time-consuming, approach of using gene transfer to insert desirable genes is one approach for improving grapevine cultivars, even considering the time necessary for field testing transgenic lines. The ability to improve the disease or pest resistance or both of a major grape cultivar (e.g., `Thompson Seedless`) offers the possibility of improving a large portion of the grape production in a relatively short time, assuming that cultivar integrity would not be compromised by the transgene or the insertion event. Such a change could also reduce pesticide use for a significant portion of grape production.